#  斐波那契
def move(n, a, b, c):
    if n == 1:
        print(f"{a} --> {c}")
        return
    move(n-1, a, c, b)
    print(f"{a} --> {c}")
    move(n-1, b, a, c)


move(2, 'a', 'b', 'c')
